1. Field of the Invention
The present invention relates to optical storage systems and control methods for optically recording and reproducing information in or from a removable medium such as an MO cartridge, and in particular, relates to optical storage systems and control methods for ensuring speed-up, stability, and safety in focus pull-in.
2. Description of the Related Arts
Conventionally, in an optical storage system known as an optical disk drive using an MO cartridge medium, when the data recorded in the medium is to be read out or when data is to be recorded in the medium, focus control for concentrating an optical beam on a recording medium which is on the medium is required.
In order to perform the focus control, first, it is necessary to learn the position at which the optical beam is currently concentrated. However, a focus error signal (FES) is not output when the position at which the optical beam is concentrated is away from recording layer. Therefore, a lens actuator is moved to an area in which the beam can be concentrated at the position near the recording layer of the medium, and focus pull-in process for closing a focus servo loop is performed at the point when focus zero-cross is detected.
In the focus pull-in process, the focus error signal is output even when the concentration position is at the surface (protective surface of the recording layer) of the medium. Therefore, generally, the lens actuator is once caused to approach the medium by the degree that it does not hits the medium, and then, the lens actuator is slowly lifted down and the pull-in process is performed at the point when the focus zero-cross is first recognized.
However, in such conventional optical storage system, in some cases, a medium goes into the movement rage of the lens actuator due to, for example, a chucking state upon insertion of the medium or warpage of the medium per se. In those cases, when the lens actuator is caused to approach the medium for performing the focus pull-in process, at worst, the lens actuator comes in contact with the medium and the medium may be damaged.
More specifically, the lens actuator is supported by a carriage by means of a spring, and, in a state in which current is not caused to flow in the drive circuit, the deviation between the position of the optical beam focal point and the position of the recording layer of the medium is designed to be about 50 μm. Therefore, in the focus pull-in control, first, the lens actuator is moved toward the medium by about 300 μm, and the lens actuator is slowly moved therefrom toward the opposite direction by about 600 μm. During this period, the focus servo loop is closed at the point when the zero-cross of the focus error signal is detected, thereby maintaining the focal point on the recording layer of the medium. The problem herein resides in that whether the lens actuator comes in contact with the medium when the lens actuator is moved in the direction toward the medium by 300 μm.
Conventionally, a countermeasure is taken by providing a clearance for avoiding the contact, however, the clearance cannot be reserved in a recent thinned system. Responding to such problem, the standards of mediums are made more strict and the height of optical storage systems are increased in order to prevent the contact between a medium and a lens actuator. However, recently, the importance of down-sizing and thinning of the systems is further rising, and there is a need to avoid the contact between a lens actuator and a medium in a focus servo pull-in process without making the standards of mediums more strict and increasing the height of the optical storage systems.